1. Field of the Invention
The present invention relates in general to alternators, and in particular to an alternator and regulator system used in a motor vehicle. Still more particularly, the present invention relates to an alternator providing current to large loads in a motor vehicle.
2. Background Information
The typical alternator contains a three-phase AC generator, a three-phase full-wave rectifier, and a voltage regulator. The engine driven alternator as used in the motor vehicle typically includes a battery which provides stand-by power at a DC voltage of a predetermined low magnitude (normally 14 volts) between a main power terminal and system ground. In such service, storage batteries are connected across the load to provide starting power for the engine, and to supply a reserve of power when the alternator output may fall short of the load demand level when the engine is operating at idle. There are stator windings within the three-phase AC generator across which a three-phase AC voltage is produced at an amplitude determined by the amount of current fed through a field winding surrounding a rotor core. The rectifier acts to convert the three-phase AC voltage to a DC voltage between the main power terminal and system ground for charging the battery and for supplying the other DC voltage vehicle loads. The voltage regulator is responsive to the DC voltage appearing between the main power terminal and system ground to control the amount of current fed through the field winding of the generator so as to cause the three-phase AC voltage output by the stator windings of the generator to have an amplitude correct to establish and maintain the DC voltage at the predetermined low magnitude.
Power output of an AC generator is usually effected by controlling the magnitude of the field current to the exciter windings of the generator. The regulator controls the voltage output to the excitation coil, or field winding, according to the effect of the load demands of the connected devices to the system voltage. If the load on the generator increases, causing a drop in the predetermined low magnitude voltage, that condition is detected by a voltage regulator and the field current is increased, causing the output voltage of the alternator to return to the predetermined voltage. Similarly, if the load on the generator is reduced, causing the voltage to increase above the predetermined low magnitude voltage, the magnitude of the field current is reduced, thereby decreasing the output power of the alternator.
The input voltage supplied to the voltage regulator is typically common to the rectified positive output of the stator windings, the load positive connection, and the battery positive terminal. Since all voltage regulators contain components that experience voltage drops across their circuits, the maximum voltage output of the regulator into the field excitation coil is always less than the voltage output of the alternator. The amount of voltage drop varies according to the efficiency of the regulator, varying from 0.8 volts to 2.5 volts.
One common type of motor vehicle having extraordinary power drains on the alternator are emergency vehicles. Often, the tremendous loads created by the multiple lights, radios, monitors, medical equipment, and safety equipment seen on ambulances, fire trucks, and modern police vehicles can create sufficient loads on the generator to significantly drop the voltage seen at the battery terminals. These power drains typically exceed the 160 amps output available from high output commercial alternators currently available. This creates severe power drain on the batteries and large stresses on the alternator. These conditions make the battery and alternator susceptible to failure. This will place the emergency vehicle out of service frequently and may present dangerous problems if such failure occurs while the vehicle is involved in an emergency situation.
This has created a need for a reliable high power output alternator. Although some advances have been made, current high output alternators don't provide sufficient power, are too expensive to make, or are too bulky to implement. Recognizing that enhancing the power output is based on the principle that the output of the three-phase AC generator is directly proportional to the current fed through the excitation coil, much effort is gone into maximizing the voltage applied to the coil and in reducing the resistance of the coil itself. With an optimum system for a self-excited alternator, prior art systems have been limited to the DC output of the alternator as a maximum excitation voltage. Moreover, rotor coil resistance has been reduced to as low as 2 ohms so that further reductions in resistance are also impractical. In most alternator systems, these limitations have been accepted, and the alternator performance has been limited by economically compromising a balance of these alternatives.
A few inventors have recognized that increasing the field excitation voltage beyond the regulated alternator output voltage would greatly improve the output of an alternator. The Schneider patent, U.S. Pat. No. 4,214,198, increases alternator rectified output voltage to 28 volts and thereby increases available rotor excitation voltage and total power output. A step down transformer is then used to reduce the operating system voltage to 14 volts. This system is very bulky and expensive due to the additional transformer.
The Severing patent, U.S. Pat. No. 4,314,194, addresses the increased rotor excitation voltage alternative with a complicated system of multiple stator windings connected in series to separate rectifier networks to increase available voltage to the regulator feeding the field excitation coil, while maintaining regulated system voltage at a lower level. This approach cannot be easily retrofitted to existing systems, and is bulky and expensive to implement in a high-output alternator due to the additional stator coils required. Severing complicates the alternator with dual wound stators which limit the alternator potential by consuming stator core space with windings dedicated to exciting the rotor. This reduces the core space available for output power winding coils.
The Stroud patent, U.S. Pat. No, 4,454,464, addresses the increased rotor excitation voltage alternative with a system which uses capacitors and relay switches to remove the voltage regulator from the circuit under full load, and feed alternator output voltage to the rotor coil without the voltage drop through the regulator. The series action of the capacitors further increases the rotor voltage from 14 volts up to as high as 17 to 20 volts depending upon rpm. In actual use, this system causes severe headlight flicker from the frequent switch-over from regulated field voltage to unregulated enhanced voltage totally dependent upon load to maintain voltage level. This unresolved voltage flicker has caused rejection of these devices by the marketplace.
The present invention provides a cost effective system for significantly increasing regulated rotor excitation voltage. Moreover, additional transformers or additional multiple stator windings are not required, and so, the bulk or complexity of the alternator unit does not have to be increased. The present invention only requires a redesigned voltage regulator and the addition of a voltage multiplier. This makes the high output alternator of the present invention inexpensive to produce, extremely reliable, and easily retrofitted into existing alternators.